The alkylation of paraffins with olefins for the production of alkylate for gasolines can use a variety of catalysts. The range of suitable process conditions that result in products with high octane and desired selectivity depends on the choice of catalyst.
Ionic liquids are catalysts that can be used in a variety of catalytic reactions, including the alkylation of paraffins with olefins. Ionic liquids are primarily mixtures of salts which melt below about 100° C.
Ionic liquids comprise an organic cation and an anion where the anion is usually an inorganic anion. Ionic liquids are described in U.S. Pat. No. 4,764,440, U.S. Pat. No. 5,104,840, and U.S. Pat. No. 5,824,832 for example. The properties vary extensively for different ionic liquids depending on the cation and the anion. The use of ionic liquids depends on the properties of a given ionic liquid. In addition, the behavior of an ionic liquid may vary considerably for different temperature ranges.
Some alkylation processes utilize low temperatures, typically 10° C. or less, which generally requires chilled cooling fluid for the reactor and/or reactor feeds. This adds substantial cost in the form of additional equipment and energy usage. In some alkylation processes, isoparaffin to olefin (I/O) ratios of 20:1 or greater are used. However, high I/O ratios like these are not desirable from an operating standpoint because they increase the cost of operation, for instance, by requiring larger reactors and more energy for distillation of isoparaffin per unit of alkylate product. Some alkylation processes use ionic liquids having low viscosity (e.g., less than 25 cSt at 25° C.), such as 1-butylpyridinium heptachloroaluminate, 1-butyl-3-methylimidazolium heptachloroaluminate, and triethyl ammonium based ionic liquids. The kinematic viscosity of these ionic liquids was measured in a comparative example herein and determined to be 21.5, 15.0 and 16-19 cSt at 23-25° C. respectively. Viscosity measurements of other halometallate ionic liquids are available in literature, for instance in Okoturo, O. O; VanderNoot, T. J; Journal of Electroanalytical Chemistry, “Temperature dependence of viscosity for room temperature ionic liquids”, 2004, vol. 568, pp. 167-181.
U.S. Pat. No. 7,432,408, U.S. Pat. No. 7,432,409, U.S. Pat. No. 7,531,707, and US 2007/0225538 broadly disclose alkylation processes using chloroaluminate ammonium, pyridinium and imidazolium ionic liquids with I/O ratios in the range of 1 to 100, catalyst volume in the reactor in the range of 2% to 70%, reaction temperatures in the range of −40° C. to 150° C., and residence times of a few seconds to a few hours. However, the Examples use low viscosity (e.g., less than 25 cSt at 25° C.) ionic liquids including 1-butylpyridinium heptachloroaluminate, and 1-butyl-3-methylimidazolium heptachloroaluminate. The viscosity of several of the ionic liquids used is unknown, including 1-butyl-4-methylpyridinium heptachloroaluminate, 1-H-pyridinium chloroaluminate, and tributyl-methyl-ammonium chloroaluminate. Based on related ionic liquids, the viscosity of 1-butyl-4-methylpyridinium heptachloroaluminate is believed to be below 40 cSt. In addition, the Examples show an I/O ratio of 4, and a temperature of 50° C. for the isopentane and ethylene alkylation. For the isopentane/propylene alkylation and isobutane/isobutene alkylation, an I/O ratio of 8, and a temperature of 10° C. were used. There are no examples for alkylation using propylene or butene at temperatures greater than 10° C., and no discussion of the problems associated with operating at those temperatures.
US 2004/0133056 describes an alkylation process utilizing alkyl-containing ammonium or pyridinium ionic liquid combined with metal compounds of Groups IB and IIB and transition metals. The broad reaction conditions include an I/O ratio of 1:1 or greater, a reaction temperature in the range of −20° C. to 100° C., and a reaction time of 2 sec to 60 min. The ionic liquids used in the Examples were low viscosity (e.g., less than 25 cSt at 25° C.) ionic liquids including triethylammonium chloroaluminates combined with copper chloride, nickel chloride, copper nitrate, and copper sulfate. Most Examples were run at low temperature (less than 10° C.: Ex. 6, 7, 11, 13, 14, 16, and 18) or high I/O ratios (30:1 or more: 10, 12, 13, 14, 16, 17, and 18). The only Examples having I/O ratios of 20:1 or less were run at low temperature (less than 10° C.: Ex. 6, 7, and 11), the reaction products had low C8 content (Ex. 6-9), and/or had low TMP/DMH ratios (Ex. 6-9, 11, and 15).
US2007/0142676 describes an alkylation process for isopentane and ethylene using pyridinium-based ionic liquids. The broad conditions include a reaction temperature in the range of −20° C. to 200° C., and a reaction time of 0.1 min to 24 hr. The I/O ratio in the example was 3.2, and the ionic liquid was 1-butylpyridinium heptachloroaluminate.
US 2009/166257 describes an alkylation process utilizing chloroaluminate ammonium, pyridinium, and imidazolium ionic liquids. The broad conditions include an I/O ratio in the range of 1 to 100, a catalyst volume in the reactor of 2% to 70%, a reaction temperature in the range of −40° C. to 150° C., and a residence time of a few seconds to a few hours. The Examples showed a 1-butylpyridinium chloroaluminate ionic liquid, a catalyst volume of 10-15%, and a temperature of 0° C.
US 2012/0178982 describes the alkylation of isobutane and/or isopentane with an olefin having 2 to 8 carbons using an alkyl-containing ammonium, imidazolium, or pyridinium ionic liquid. The I/O ratio is 1:1 or greater, with high I/O ratios being preferred, e.g., at least 20:1, more preferably at least 50:1, even more preferably at least 100:1. The reaction temperature is in the range of −20° C. to 100° C. No examples are given.
US2012/0283500 describes the alkylation of isobutane and butene using alkyl-containing ammonium, imidazolium, or pyridinium ionic liquids. The examples used ionic liquids containing triethylammonium (Et3NH) and 1-butyl-3-methylimidazolium cations, and anions containing chlorohexabromoaluminate or heptachloroaluminate, with some including various copper compounds. The Examples show I/O ratios of 10:1 to 40:1, and temperatures of 20° C. to 30° C. The olefin feed rate for Examples 3-8 and Comparative Examples 1-2 was calculated from the information given to be less than 0.2 g olefin/g ionic liquid/hr (1.4 mol olefin/mol ionic liquid/hr). The olefin feed rate cannot be calculated for Examples 1a-b and 2a-b because no feed rate or olefin feed rate is given for those examples. However, assuming these feed rates were the same as that in Example 4, the olefin feed rate would be less than 0.2 g olefin/g ionic liquid/hr (1.4 mol olefin/mol ionic liquid/hr). In addition, no volume fraction of ionic liquid or residence times are given.
US Application Serial Nos. 2013/0345484 and 2014/0113804 teach that certain phosphonium ionic liquids having a kinematic viscosity greater than 50 cSt at 20° C. are preferable because they result in higher octane than do lower viscosity ionic liquids, and that this advantage is larger at higher operating temperatures. However, the olefin was added with a slow flow rate (0.5 g olefin/g ionic liquid/hr or 5.2 mol olefin/mol ionic liquid/hr), leading to long residence times (e.g., about 115-120 min) Such long residence times are not desirable for commercial practice as they would require very large reactors or very small product production rates.
Therefore, an alkylation process utilizing ionic liquids that does not require operation under more extreme conditions such as refrigeration or long residence times would be desirable.